Boat lifts are presently available for side-mooring and bow mooring boats to a sea wall or dock. While stern-mooring of a boat on a lift would be very convenient for boarding and disembarkment, stern-moored boat lifts are not presently known. The motion and positioning of side and bow mooring lifts during operation prevent their use for stern mooring.
Side mooring lifts cannot be used for stern mooring because during operation, their motion is controlled by guides connecting the lift to the sea wall or dock both fore and aft. As the lift is operated, the bow and stern do not move together. During lowering, air is initially evacuated from one end of the lift tanks as water enters the other end, causing the lift to displace angularly downwardly about the air outlet end. As the water volume in the tank increases, the air outlet end also lowers and the tank returns to a level condition. The process is reversed when the lift is raised. To accommodate this angular motion, the guide components connecting the lift to the sea wall or dock are constructed to function independently so that the portion of the lift connected to the sea wall or dock is free to reciprocate independently. A stern-moored lift cannot be permitted to displace angularly or list on its guide components. The guide components must work in unison with each other to maintain the lift in a laterally level condition while the bow and stern each displace angularly.
Bow mooring lifts cannot be used for stern mooring either. They are generally pivoted at the sea wall or dock so that the bow end remains elevated while the stern end is lowered to receive the boat, bow first. Consequently, if bow mooring lifts were used for stern mooring, the aft portion of the boat, and especially the propeller, would strike the bow end of the lift.
It is, therefore, an object of this invention to provide a boat lift for stern mooring boats to sea walls and docks. Another object of this invention is to provide a boat lift having stern mounted guides for controlling the operational motion of the lift. A further object of this invention is to provide a boat lift having guide components which limit lateral movement of the lift in relation to the sea wall or dock. Yet another object of this invention is to provide a boat lift having guide components which, when stern mounted to the sea wall or dock, allow the stern to move freely vertically in relation to the sea wall or dock. It is also an object of this invention to provide a boat lift having stern mounted guide components which function to allow vertical reciprocation of the stern portions of the lift tanks in unison with each other.
In accordance with the invention, a lift for mooring a boat stern-on to a sea wall or dock is provided. A pair of horizontally spaced guide members fixed to the sea wall extend from the sea wall to a vertical plane parallel to the sea wall. A pair of substantially parallel hydro-pneumatic buoyancy tanks are symmetrically spaced from a vertical plane which is perpendicular to the parallel plane and extends substantially midway between the guide members. A frame is fixed to the tanks to provide a flotation platform for supporting the hull of the boat. The keel of the boat is received substantially aligned with the perpendicular plane and the stern of the boat is received at the stern end of the platform near the sea wall. Each of the tanks is connected to the guide members. The guide members limit movement of the platform away from the parallel plane or sea wall and away from the perpendicular plane or laterally along the sea wall. The guide members also operate in unison to restrict the lift from listing during operation.
In one preferred embodiment, a pair of horizontally spaced vertical tracks are fixed to the sea wall proximate their upper ends. They extend from the sea wall to a vertical plane parallel to the sea wall. A pair of slides are each fixed at one end to the stern ends of each of the tanks. They each engage and ride at their other end on the tracks. The slides limit movement of the platform away from the parallel plane or sea wall and away from the perpendicular plane or laterally along the sea wall while permitting the stern of the platform to reciprocate in unison vertically along the tracks. Preferably, the slides have pivoting linkages facilitating vertical displacement of the tanks relative to the guide members and restricting lateral displacement of the tanks relative to the guide members. The pivoting linkages each preferably have a clevis fixed to the slide, a bracket fixed to the tank and a link pivotally connected at one end to the clevis and at the other end to he bracket,. The links are formed from elastomeric material. The tracks are I-beams with their webs disposed in the vertical plane. The slides are members of C-shaped cross-section engaged on flanges of the I-beams. An anchor may optionally be disposed on the sea floor forward of the tanks and substantially aligned on the perpendicular plane. A line connected between the anchor and the bow portion of the platform at substantially the mid-point between the tanks limits movement of the bow end of the platform away from the perpendicular plane or laterally along the sea wall.
In another preferred embodiment, a pair of horizontally spaced rings fixed to the sea wall extend from the sea wall to the vertical plane parallel to the sea wall. An anchor is disposed on the sea floor forward of the tanks with a line connecting the anchor to the bow portion of the platform. One pair of lines is connected between each of the rings and the bow end of its corresponding tank. A second pair of lines may also be connected between each of the rings and the stern end of its opposite tank or between each of the rings and the opposite sides of the stern of the boat. The anchor line and the first pair of lines limit movement of the platform toward and away from the parallel plane or sea wall and laterally along the sea wall while permitting the stern of the platform to reciprocate vertically in unison along the tracks. The second pair of lines assist in restricting lateral movement of the platform along the sea wall when the lift is not in operation but must be cast off before operation of the lift.